RFR: 8203359: Container level resources events [v2]

[Jaroslav Bachorik]

> With this change it becomes possible to surface various cgroup level metrics (available via `jdk.internal.platform.Metrics`) as JFR events.
> 
> Only a subset of the metrics exposed by `jdk.internal.platform.Metrics` is turned into JFR events to start with.
> * CPU related metrics
> * Memory related metrics
> * I/O related metrics
> 
> For each of those subsystems a configuration data will be emitted as well. The initial proposal is to emit the configuration data events at least once per chunk and the metrics values at 30 seconds interval. 
> By using these values the emitted events seem to contain useful information without increasing overhead (the metrics values are read from `/proc` filesystem so that should not be done too frequently).

Jaroslav Bachorik has updated the pull request incrementally with one additional commit since the last revision:

  Split off the CPU throttling metrics

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3126/files
  - new: https://git.openjdk.java.net/jdk/pull/3126/files/9ba3c5a6..90de0d8c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3126&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3126&range=00-01

  Stats: 88 lines in 3 files changed: 73 ins; 15 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3126.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3126/head:pull/3126

PR: https://git.openjdk.java.net/jdk/pull/3126